Semiconductor devices, such as integrated circuit chips, are electrically connected to leads on a lead frame by a process known as wire bonding. The wire bonding operation involves placing and connecting a wire to electrically connect a pad residing on a die (semiconductor chip) to a lead in a lead frame. Once all the pads and leads on the chip and lead frame have been wire bonded, it can be packaged, often in ceramic or plastic, to form an integrated circuit device. In a typical application, a die or chip may have hundreds or thousands of pads and leads that need to be connected.
There are many types of wire bonding equipment. Some use thermal bonding, some use ultra-sonic bonding and some use a combination of both. Prior to bonding, vision systems or image processing systems (systems that capture images, digitize them and use a computer to perform image analysis) are used on wire bonding machines to align devices and guide the machine for correct bonding placement.
Machine vision systems are generally used to inspect the device before, during or after various steps in the fabrication process. During such process steps, it may be necessary to obtain multiple views of the device under different magnification levels to determine whether the device meets predetermined quality standards. One measurement may require a large field of view to include as many fiducials as possible, while a second measurement may require a high resolution to image fine details. Further, these various measurements may need to narrow or expand the depth of field of the observed object in order to view certain details.
In conventional systems, such multiple magnifications are handled by having a separate camera for each desired magnification level. Such a conventional device is shown in FIG. 1. In FIG. 1, imaging device 100 includes objective lens 104, aperture 106, beam splitter 108, mirror 110, relay lenses 112, 114, and cameras 116, 118. In operation an image of device 102 is transmitted through object lens 104 as transmitted image 120 and in turn through aperture 106 as image 122. Image 122 is incident on beam splitter 108, which in turn divides the light from image 122 into first divided light rays 124 and second divided light rays 126. Divided light rays 126 are then redirected by mirror 110 as divided light 128.
Relay lenses 112 and 114 are selected so as to provide the desired magnification of divided light 124 and 128, respectively, resulting in magnified images 130 and 132, which are incident on cameras 116 and 118, respectively. This system has drawbacks, however, in that it requires a separate camera for each level of magnification desired, and also require that multiple apertures be provided to handle different depths of field, thereby resulting in greater complexity and increasing size and cost.
A second conventional system is shown in FIGS. 2A and 2B. In FIGS. 2A and 2B, a shutter 218 is used in combination with a second beam splitter 222 to receive two magnifications of device 202 with a single camera 216. As shown in FIG. 2A, first beamsplitter 208 separates light rays 224 into light rays 226, 228, each being of about equal illumination, that is each of light rays 226, 228 is about half the illumination of light rays 224. When shutter 218 is in a first position, light rays 226 are prevented from reaching relay lens 214. On the other hand, light rays 228 are magnified by relay lens 212 to become magnified light rays 230. In turn, magnified light rays 230 are incident on second beamsplitter 222, a portion (about 50%) of which is transmitted to camera 216 as light rays 236. The remaining portion of magnified light rays 230, however, is deflected by second beamsplitter 222 as lost light rays 234. As a result, only about 25% of the light used to illuminate device 202 is actually received at camera 216. In addition, the inclusion of shutter 218 increases the complexity and cost of this system.
Alternatively, and as shown in FIG. 2B, when shutter is in a second position, light rays 228 are prevented from reaching relay lens 212, while light rays 226 are directed through relay lens 214 by mirrors 210, 220 as magnified light rays 232. Similar to FIG. 2A, a portion 236 of magnified light rays 232 are received by camera 216 while remaining light rays 234 are lost. As is evident, a large portion of the illumination available for imaging is sacrificed due to the losses associated with first beam splitter 208 and second splitter 222. The light from a single channel hits the second splitter and is split into a reflected portion 234 and transmitted portion 236. Only one of these will be directed to camera 216 while the other is lost. This approach can also have reliability issues with respect to the moving shutter mechanism.